1. Field of the Invention
The present invention relates to a particulate matter (PM) oxidizing catalyst. More in detail, the present invention relates to a PM oxidizing catalyst capable of continuously oxidizing or combusting PM from a relatively low temperature during an engine operation.
2. Description of the Related Art
Conventionally known method for a diesel engine includes the following operations. An electric power and the like is inputted to a collected particulate matter (PM) or fuel is consumed to thereby increase temperature of the collected particle, then, oxidation or combustion reproduces a particulate filter. However, the reproduction by the electric power and the like requires a great energy quantity, while the reproduction by the fuel decreases fuel economy (i.e., increasing fuel consumption) of the engine.
With the above background, a catalyst capable of oxidizing PM at a relatively low temperature to thereby decrease the consumed electric power and improve fuel economy is used, and the material and component of such catalyst are improved.
U.S. Pat. No. 6,355,220 (family of laid-open JP2000507877T and examined JP3657620) proposes use of Cex—Zry—Prx (x=0 mol % to 0.3 mol %) as 3-way catalyst.
Moreover, EP1504815 (family of laid-open JP2003334443=examined JP3528839) proposes use of Ce—Zr-M (M=La, Sm, Nd, Gd, Sc, Y).
However, for oxidizing the PM from a relatively low temperature, the above conventional methods each have a room for improvement.